Year	% of revenue
1972	24.198086662915024
1973	27.537593984962406
1974	34.59605720912254
1975	36.904005085823265
1976	34.20107719928186
1977	33.907012586694066
1978	31.013110846245528
1979	28.95436873337426
1980	32.49018067556952
1981	35.03911760933692
1982	36.746189529489726
1983	32.58344764517604
1984	30.145838791371933
1985	26.959509658246656
1986	20.910575352992026
1987	19.108673824051902
1988	20.915127020785217
1989	24.31572246976448
1990	25.609892569382275
1991	26.959184698027013
1992	28.47403603523839
1993	25.96191493148247
1994	26.49070021881838
1995	25.557752047444225
1996	23.919232391396037
1997	23.80462853847504
1998	24.68403605096861
1999	24.9764443342425
2000	29.026494581188146
2001	31.575319735532126
2002	30.97150997150997
2003	29.604188101434364
2004	27.556273618489513
2005	30.16579158368466
2006	31.18582312023849
2007	28.45604343270788
2008	34.43361645060349
2009	35.66994040821411
2010	33.9853675074092
2011	34.36466453310861
2012	34.71643602025158
2013	33.129315165116054
2014	33.26258102206025
2015	32.651031326230814
2016	32.3621645333085
2017	33.457463527320705
2018	33.27790841578012
2019	30.251497657353166
2020	37.88716962378073
2021	36.920946844798934
2022	37.805401400189034